Helpful Questions & Answers

Answer

To determine the correct stresses, it is necessary to know the local coordinate system of the surface. You can activate it in the Display navigator under “Model” -> “Surfaces” -> “Surface Axis Systems x, y, z.” All stresses with an “+” in the index indicate the stress at the top surface, that is, the side of the positive local z-axis. When showing the surface moments, notice that there is a fundamental difference between surface and member internal forces: While the member moment My about the local member axis y “rotates,” a surface moment my is acting in the direction of the local surface axis y, that is, about the axis x of this surface.

For the given example, this means that the bending moment of the lap joint is acting in the direction of the global y-axis and therefore has to have a value of 2 kNm/m as result. The average in the depicted diagram confirms this assumption by a value of 1.95 kNm/m (deviations can be reduced by a finer FE mesh). The average of the shear flow is 100 kN/m and therefore corresponds to the applied load.

The stress sigma-y,+ thus represents the compressive stress of the lap joint at the top surface and tau-xy,x represents the shear stress in the interface on the same side.

Keywords

weld, weld stress, internal forces in surfaces

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